双复杂介质条件下频率空间域有限差分法保幅偏移

油气勘探的重点正转向复杂地表条件和复杂地质条件的区域.双复杂条件下的叠前深度偏移是解决复杂地表条件和复杂地质构造成像的有效手段.基于“逐步累加”的“直接下延”法是解决复杂地表成像的有效手段，能够较好地消除地形起伏的影响.波动方程频率空间域有限差分(xwfd)叠前深度偏移对介质速度横向变化有较强的适应性，适宜于复杂构造的偏移成像，同其他常规波动方程深度偏移一样，常规的xwfd偏移方法，主要也是针对相位进行波场延拓，没有对振幅做任何处理.我们基于保幅单程波方程，推导出了基于xwfd的保幅波场延拓算子，针对xwfd求解时引入误差的影响，我们在xwfd保幅波场延拓过程中加入了误差补偿，实现了带误差补偿的xwfd保幅偏移.基于带误差补偿的xwfd保幅算子，应用适合起伏地表的直接下延法，对双复杂介质模型和实际资料进行了试算，改善了双复杂介质的成像效果.其中，误差补偿可以在若干个外推步长上进行，所以相对于保幅傅里叶有限差分(ffd)法偏移来说，该方法在改善成像质量的同时，也具有较高的运算效率.

Preserved-amplitude migration with dual-complexity

Oil and gas exploration is turning to the areas with irregular topography and complex geologic structures.Prestack depth migration turns out to be a valid way to deal with irregular topography and complex geologic structures."Wave field downward continuation" based on accumulating step by step is a valid way to solve the problem of irregular surface migration.Xwfd pre-stack migration based on wave equation has strong adaptability to the medium which has strong variable transverse velocity and it can be used for migration with dual-complexity.Similar to other conventional migration,it makes just continuation of phase and does nothing to the amplitude.We derived the preserved-amplitude xwfd one-way wave equation operator and added the error compensation caused when solving the wave equation.Based on the xwfd error compensation preserved-amplitude operator,we use the method of "wave field downward continuation" to process the dual-complexity model and real seismic data.The impulse response test and the results of the prestack depth migration for model and real seismic data show that the method is an effective tool for dual-complexity.The error compensation can be done during several continuation steps,compared to conventional Finite Difference Fourier(fft)it has better migration quality.